1. Field of Invention
This invention relates to devices that may be varied between bendable and stiffened states, and more particularly to such stiffenable assemblies in tubular arrangements in devices for minimally invasive surgery.
2. Art
Minimally invasive surgical tools, such as those used for laparoscopic surgery, are often substantially rigid. Consequently, their reach is limited. To achieve useful triangulation of instruments at an internal surgical site, instruments must be inserted through multiple ports in the patient's body wall.
Flexible endoscopes that allow passage of two or more instruments to an internal surgical site are being used for surgery because such use requires only a single entry port into the body. But endoscopes typically lack rigidity and lack instrument triangulation at the distal end of the endoscope. Since the surgical instruments experience reactive forces from tissue (e.g., when retracting, suturing, etc.), some endoscopes rely on bracing against surrounding tissue to provide a stable base for the instruments. Other endoscopes rely on a stiffening/rigidizing mechanism. For instance, cables used to steer the endoscope may be locked in position or tensioned to increase friction in the endoscope's joints in order to stiffen the endoscope. But surrounding tissue used for bracing may be soft, and small control cables are subject to stretching due to the moment loads at the endoscope's distal end. Accordingly the flexible endoscope may only be made a limited amount more stiff than its flexible state. In addition, longitudinal tension on control cables used to increase friction between an endoscope's joints may cause the distal tip of the endoscope to move.
What is desired, therefore, is a structure that is significantly stiffer in a rigid state than in a flexible state. It is further desired that the structure be rigidizable in various shapes—bent or straight—and that such rigidizing does not affect the shape.